A great number of electrical and electronic devices are made in portable configurations. Many devices, such as cellular phones, for example, have gained widespread market acceptance. Indeed many personal as well as business tasks are performed with cellular phones, portable computers, personal digital assistants, and similar devices. The convenience afforded by this portability has significantly increased the speed at which business is conducted. For example, business travelers may now engage in conference calls, receive and reply to correspondence, and perform database searches while traveling. These are functions which were previously performed exclusively from an office.
To enable portability of a given device, a suitable and equally portable power source must be developed. Batteries and battery packs are typically used to fulfill this need. The two main factors to be determined in selecting an appropriate battery design are how much power must be provided, and for how long. These factors determine the resulting size of the energy source and type of electrochemical system used. Often the size of a battery pack for a given device is substantial, and may rival the size and weight of the device itself. Accordingly, there is an effort in the industry to reduce the size of battery systems. To accomplish this goal, designers have adopted a system approach.
In general there are three areas being addressed in portable systems to reduce battery or battery pack size. The first area is in reducing the power demand of the device. This is achieved, in part, by increasing the efficiency of it's circuitry. The second area is in increasing the energy density of electrochemical systems used to make batteries and battery packs, and developing new systems with much higher energy densities compared to conventional systems. New systems are being developed which provide much more capacity than conventional systems such as nickel cadmium, lithium ion being the most recent example. The third area is in optimizing the use of battery power. This has come be known as "smart battery" technology.
The term "smart battery" generally refers to a battery pack having some electronic circuitry which facilitates more efficient use of the stored energy. For example, many circuits have been developed which provide a state of charge or "fuel gauge" indication for the device. The user of a portable computer, for example, can configure the computer to sacrifice speed of operation for efficiency of operation. Circuitry is sometimes necessary when selecting more energy dense electrochemical systems, such as lithium ion, to ensure reliable operation under a variety of conditions. Circuits have been developed which shield the battery cells from stressful electrical events, and help prolong and enhance performance. As one would expect, the addition of electronics to a battery pack increases the cost of the battery pack. In view of the fact that these circuits add value in terms of operation and safety, many consumers have readily agreed to pay for the additional cost.
Still, some consumers may find the additional cost in the battery pack prohibitive. If possible, it would be a market advantage to reduce the cost of a smart battery pack to the consumer, while still providing the appropriate battery electronics. In order to achieve this, however, it is not enough to simply find less expensive components. A fundamental change of perspective is required.
In manufacturing battery packs having electronic circuits, the circuit is formed as an integral part of the battery pack. The circuit is placed permanently inside each battery pack. However, the battery cells in the pack have a finite and relatively short life span. Typically, rechargeable battery cells last about 2 years with moderate usage. When the battery cells are no longer useful, the entire battery pack is disposed of, including the circuit. However, electronic circuits have a much longer life than battery cells. Further, most users buy more than one battery pack, which means they buy the same circuitry twice. Therefore, there is a need for reducing the cost of a battery pack with a means by which an electronic battery circuit can be re-used, and shared, thus eliminating the need to re-purchase circuitry.